Altimeter control device



1942- F. e. NESBITT ALTIMETER CONTROL DEVICE File d Aug. 15. 1938' 4Sheets-Sheet I Nov. 3, 1942. F. G. NESBITT ALTIMETER CONTROL DEVICEFiled Aug. 15, 1938 4 Sheets-Sheet 2 ANT. mm.

fox/vars Nov. 3, 1942. F. G. NESBITT 2,300,432

ALTIMETER CONTROL DEVICE Filed Aug. 15 1938 4 Sheets-Sheet 3 Awe/v ranFEA/VGAS GLEN Mess/r7 Patented Nov. 31, 1 942 ran coon DEVICE FrancisGlen Nesbitt, Dayton, Ohio Application August 15, 1938, Serial No.224,969

(Granted under the act of March 3, 1883, as amended April 30, 1928; 3700.- G. 757) Claims.

The invention described herein may be manufactured and used by or forthe Government for governmental purposes, without the payment to me ofany royalty thereon.

The present invention relates broadly to means for determining altitude,and more particularlyfor determining the altitude of aerial bodies.

More specifically, the invention relates to altimeters for aircraft andcorrelated ground equipment. It proposes an apparatus of. this classwhich will give an accurate indication of the height of the craft abovethe ground or terrain over which the craft is moving, or its heightabove sea level.

It is an object of my invention to provide a means to further increasethe usefulness, depend-' ability, and accuracy of pressure altlmetersand temperature-pressurealtimeters. Pressure altimeters actuallydetermine their indication by measuring the difference in barometricpressure at the point of measurement and at the point of reference.Present day altimeters permit the point of reference to be changed inflight provided data may be obtained from the ground by radio. To obtainthis data with the present day equipment requires an attendant at eachpoint of reference.

It is a further object of my invention to provide a device whichincludes ground equipment adapted to automatically provide the referencedata to airplane equipment by radio without requiring an attendant ateach ground station. My, invention therefore permits the installation ofground reference equipment at numerous intermediate points includingdangerous mountain ranges, critical points, as well as at main controlstations, without the need for an attendant. By doing this, the personalerrors of the operators are eliminated and greater accuracy is therebyobtained, and conditions which otherwise might be a definite hazard toflying are also eliminated.

Another object of my invention is to provide means for determination ofaltitude with sufilcient accuracy to permit airmen to make blindlandings with the-aid of automatic ground equipment with which thealtimeter is coordinated.

The present invention is based upon the principle of the conventionalpressure altimeter (or temperature-pressure altimeter) in combinationwith an electrical system and radio method whereby the altimeter carriedby the aircraft may be coordinated manually by the airman with automaticequipment on a landing field or any other point of reference, whichmakes it possible to correct the setting of the altimeter forfluctuations of atmospheric pressure and temperature at diiferent timesand/or different points of reference. Thus, in substituting automaticelectrical methods for transmitting by radio the pressure andtemperature indications at the ground point of reference, refinements inapparatus and operating technique are possible.

Other objects and advantages of m invention will become apparent; fromthe following description taken in connection with the accompanyingdrawings, it being clearly understood that the same are by way ofillustration and example only and are not to be construed as in any waylimiting the spirit or scope of my invention. The spirit and scope ofthe invention is to be limited only by the terms of the appended claims.

Referring to the drawings, in which numerals of like character designatesimilar parts through out the several claims:

Fig. 1 shows a ground unit for controlling frequency-pressure altituderelation;

Fig. 2 shows a ground unit for controlling frequency-temperaturerelation;

Fig. 3 shows the front face 01 an aircraft altimeter responsive tosignals of the ground unit of F Fig. 4 shows a side elevation of Fig. 3;

Fig 5 shows the front face of an aircraft air thermometer unitresponsive to signals of the ground unit of Fig. 2;

Fig. 6 shows a side elevation of Fig. 5, partially in cross-section;

Fig. 7 shows the front face of an aircraft temperature-pressurealtimeter unit capable of joint response to signals of the ground unitsof Figs. 1 and 2;

Fig. 8 shows a side elevation in partial crosssection of Fig. 7;

Fig. 9 is a fractional bottom view of the switch shown in Fig. 8.

Fig. 10 is a cross-sectional view through the instrument illustrated inFig. 7.

Fig. 11 is a part elevational view taken generally along the lines ll-Ilof Fig. 10.

Fig. l shows, in schematic form, a ground unit for controlling thefrequency in accordance with a pre-selected frequency-pressure altituderelationship. I make use of a small radio transmitter la, the frequencyof whose signal is controlled by a pressure responsive means 2 inaccordance with the aforesaid pro-selected frequency-pressurerelationship. The pressure responsive means 2 is composed of a base 3fixed to the lower extremity of a pressure responsive element 4, ahorizontal link 5 pivbted at its left extremity toan upstanding support6 and further pivoted inboard thereof to the upper extremity of thepressure element 5 and at its right-hand extremity pivotally connectedto a vertical link I. Thus,

respectively, of a gear sector 9 pivotally secured at III to anupstanding support ll of the base 3. To eliminate backlash in thelinkage, the gear sector 3 is provided with a counterbalanced spring l2.Thus, expansion or contraction of the element 4, in response to pressurechanges in the atmosphere surrounding the same, brings aboutcounter-clockwise or clockwise rotation of a gear l3 fixedly secured onthe shaft forming an integral part of the frequency control of the radiotransmitter la. The transmitter is provided with a terminal l4 groundedat l5a, and with a terminal l6 operably connected to an antenna Ila. Ihave thus provided for continued transmission of. a suitable radiosignal automatically controlled within a pre-designated frequency bandand in accordance with a. pre-selected' frequency-pressure altituderelation bypressure variations acting upon the element 4.

In Fig. 2, the greater portion of the parts of Fig.1 are duplicated. Itshould be noted, however, that the pressure responsive means 2 isreplaced by a .free air thermometer means l8, con-.

sisting of an element 4', an exterior bulb l3 and connecting tubing 23,and that the former transmitter la, the ground I51: and the antenna llaare redesignated lb, lib and "11", respectively. Temperature increasecauses counterclockwise rotation of the horizontal link 5 about thepivgt 8, with corresponding counter-clockwise rotation of the gear l3.Temperature decrease effects opposite rotation of the gear I3. I havethus provided for continued transmission of a suitable radio signalautomatically controlled within a pre-designated frequency band and inaccordance with a pre-selected frequency-temperature relation bytemperature variations at the exterior bulb l9 acting upon the element4'. It should be noted that the frequency band for the radio transmitterlb (of Fig. 2) must be different than the frequency band for the radiotransmitter la (of Fig. 1) in order that corrections for pressure andtemperature variations be segregated.

Fig. 3 shows the front or indicating dial, and Fig. 4 a side elevationof a standard aircraft pressure altimeter unit revised in accordancewith the teaching of my invention to respond to the radio signal of theground unit of Fig. 1. It is composed of a radio receiver unit 2 la anda conventional pressure altimeter 22 mounted'in tandem relationshiptherewith. The receiver 2la is entirely encased within a housing 23provided at its forward'extremity with three mounting lugs 24 by meansof which the assembled parts are held in fixed relationship with therear extremity of the altimeter 22. The short shaft normally providedfor the setting knob (such as the setting knob 25 of Figs. 3 and 4) isreplaced (in the aforesaid figures) by an elongated shaft 26, extendingto and entering within the forward portion of the housing 23, where itis provided with a fixed driving gear 21. The gear 21 reniaining at alltimes in fixed engagement with a second driven gear 28a fixed to atuning shaft 29 of the receiver 2 la. The driving gear 21 and drivengear 28a are so interrelated that the complete range of altimeter zerosetting adjustment effected by means of the knob 25 lies well within thetuning range accomplished by means of movement of the tuning shaft 29.Thus, afany time an airman desires to effect the correct altimeterreference setting of the aircraft held altimeter to correspond to thecooperating station altimeter located upon the ground or other.reference, he has but to adjust the knob 23 backward or forward(depending upon initial temporary setting) over an unknown range ofaltimeter setting until the ground transmitter la and the aircraft heldreceiver 2! are tuned into identical frequency of radio signal asindicated by means of a signal lamp 35. when a lamp 35 lights, the "zerosetting" system of the aircraft altimeter is automatically set to theexisting conditions at the station equipment located at the point ofground reference.

' Referring to Fig. 3, a brief statement of the manner in which thezerosetting' is accomplished in the conventional altimeter 22 isbelieved desirable. Altitude isread oil. a scale 34 in a manner similarto that used in reading a water or gas meter. the thousand foot pointer,is shown closely approaching the numeral 3 on the scale 34. Thisindicates the altitude as closely approximating. though slightly lessthan 3000'feet. A hundred foot pointer 32 is shown half way between thenumerals 9 and 0, which indicates an actual reading of 950 feet. Thecombined indication of both pointers is therefore taken to read 2950feet altitude.

Reference marks 30 and 3 l, in conjunction with the setting knob 25,constitute a "zero setting" system well known to those skilled in theart of instrument flying. Both marks are read" on the fixed scale 34and'in a manner identical to "reading of the pointers 32 and 33. Thesetting knob 25, when turned manually, rotates the pointers 32 and 33and thereference marks 30 and 3|, simultaneously. During the aforesaidrotation, the pointer 32 and the reference mark 30are rotated the sameamount with reference the scale 34, but in the opposite direction. Thesame thing is true of the other pointer and reference'mark, that is,when'the thousand foot pointer 33 isrotated up 1000 feet, the thousandfoot" reference mark 3| is rotated down 1000 feet. In like manner, whenthe hundred foot pointer 32 is rotated up feet,the hundred foot"reference mark 30 is rotated down 100 feet. When both reference marksread zero, the pointers are reading altitude in the standard atmosphereabove "standard atmosphere sea level." In this way, the zero settingsystem always indicates the altitude in the standard atmosphere at whichthe pointers will read zero. As has been previously stated, the receiver2 la. has its tuning control geared directly with the altimeter settingknob 25 such that the correct zero setting" will be effected when thesignal from the ground transmitter la is tuned in as indicated by meansof the lamp 35 provided on the forward face of an altimeter mountingpanel 36.

If it be assumed that the standard temperature conditions, as defined bythe standard atmosphere, actually exist throughout the atmosphere; truealtitude will be indicated by the pressure altimeter when the zerosetting" has been mometer installed on the airplane but the groundtemperature at the ground point of reference must be obtained by radio.

A pointer 33 constituting to selectively altimeter 44. It will be noted,in Fig. 8, that a Fig. shows the front face and Fig. 6 the sideelevation of a standard aircraft free air thermometer unit to which hasbeenadded an independently operable reference mark adapted to respond toradio signals of the ground unit of Fig. 2. It consists of aconventional free air thermometer 38 provided with a ground temperaturesetting knob 39 forming a part of a system much the same in itsmechanical operation as the zero setting" system heretofore described inconnection with the altimeter 22, except that it is not connected to thepointer 59. An aircraft held receiver 2 lb, similar in its internalstructure to the internal structure of the aircraft held receiver 2 la,but differing therefrom in its frequency band, is positioned with itslongitudinal axis coaxial with the longitudinal axis of ,the thermometer38. V

In the partial cross-sectional showing of Fig. 6, a gear ring 48,supporting a reference mark 4| in rotational relation to a fixedthermometer scale 58, is shown in operative engagement with adrivlnggear 42 fixed to the shaft 43 of the setting knob 38. A seconddriving gear 42 is in operable engagement with a driven gear 28b,performing in substance the identical functions of the driven gear 28aof Fig. 4. The second gear 42 and driven gear 28b arealso sointerrelated that the ground temperature range of the thermometer scaleover which the ground temperature reference mark 4| is moved by means'ofthe knob 39-will lie well within the tuning range accomplished by meansof movement of the tuning shaft 29. Thus, at any time an airman desiresto obtain the existing ground temperature he has but to adjust the knob39 backward or forward (depending upon initial temporary setting) untilthe ground transmitter lb and the aircraft held receiver 2|b are tunedinto identical frequency of radio signal as indicated by means of thesignal lamp 35. When this is accomplished, the ground temperature may bereadily ascertained by simply noting the position of the reference mark4| with respect to the temperature scale 88.

A temperature-pressure altimeter is one which derives its indicationfrom both temperature and pressure and with this type of altimeter theabove described temperature correction is unnecessary. However, in usinga. temperaturepressure altimeter of the type disclosed in my Patent No.2,081,950, it is necessary to obtain both the ground temperature andground pressure before setting the zero setting" system. My inventionmay also be applied to this type of altimeter. Fig. 7 shows the frontface, and Fig. 8 shows a partial side elevation, of an aircrafttemperature-pressure altimeter capable of joint response to signals fromthe ground units of both Figs. 1 and 2. The separate altimeter 22 ofFigs. 3 and 4 and the thermometer 38 of Figs. 5 and 6 are replaced by asingle temperaturepressure altimeter 44. An adjusting knob 45 isprovided for alternate zero setting of either the "ground pressure" unitor the ground temperature unit of the altimeter 44. In like manner theseparate radio receiver unit Zla (of Fig. 4) and the separate radioreceiver unit 2|b (of Fig. 6) are combined into a single radio receiverunit 2|c. A toggle switch 46, automatically operated by normal (full) orinward (dot-dash), positionings of the knob 45 of Fig. 8, is utilizedtune in the aforesaid ground unit of pressure unit or ground temperaturethe radio receiver unit 2|c with corresponding alternate zero setting ofthe ground pressure unit or the "ground temperature unit of the spring41 normally holds a driving gear 48, fixed to a shaft extension 49 ofthe knob 45, in operable engagement with a driven gear 58. The gear 58is the outermost element of a gearing system by means of which zerosetting adjustment of the pressure element" of the temperature-pressurealtimeter 44 referred to above is obtained; i. e., adjustment of thereference marks 38 and 3| in relation to the fixed scale 34. It will befurther noted that the knob 45 can be inwardly pressed into the dot-dashpositioning of Fig. 8, such that the driving gear 48 is brought intooperable engagement with a gear 5| forming the outermost element of agearing system by means of which zero setting adjustment of thetemperature elemen of the temperaturepressure altimeter 44 referred toabove is obtained, i. e., adjustment of the reference mark 4|a inrelation to a fixed scale 68a. By further provision of a second drivinggear 52, fixed to the shaft extension 49 and at all times in operableengagement with a driven gear 280 of radio receiver 2|c, it is readilyobvious that the airman can effect zero setting for "pressure or fortemperature by* sole reference to the signal lamp 35 provided upon amounting panel 53 of the temperature-pressure altimeter 44. At thispoint I desire to call special attention to the fact that eithertemperature change (effecting movement of the pointer 59a) or manualshifting of the reference mark 4|a (by the setting knob 45) directlyeffects a change in the positioning (i. e., a temperature compensation)of the pointers 32 and 33 of Fig. '7.

In the instrument illustrated in Figure '7, and as previously described,compensation is made for ground pressure by actuation of knob 45 which,in turn, operates shaft 49 for tuning the receiver and simultaneouslyadjusting the movable pressure reference marks 38 and 3| by means of aseries of gears as illustrated in Fig. 10, and which will now bedescribed. Referring to that figure, gear 48 is fixedly attached toshaft 49 as previously pointed out. This gear 48, in turn, is adapted toselectively mesh with gears 58 and 5|. Actuation of knob 45 when gears48 and 58' are in mesh results in the adjustment of the reference marks38 and 3| as well as pointers 32 and 33. The gear arrangement foraccomplishing actuation of reference marks 38 and 3| will be describedfirst as follows:

Gear 58 is fixedly attached to shaft 88 which, in turn, passes throughand has bearing engagement with frame member 88a. Also fixedly attachedto shaft 88 at one end thereof are a pair of planetary gears 8| and 82which have a ratio relationship .of 1 to 10. Gear 82 meshes withinternal gear 3Ia for operating the same, and consequently referencemark 3| which is integral therewith. Gear 8| meshes with internal gear38a for operating the same, and reference mark 38 which is integraltherewith. Actuation of knob 45 to adjust pointers 32 and 33 isaccomplished by intermeshing gears 48, 58 and I88, the latter of whichis rigidly attached to one end of shaft I8I. At the other end of thisshaft is a gear I82 adapted to mesh with gear I83 freely rotatablymounted on pointer shaft |I3a. Gear I83 is adapted to mesh with gear||l4 fixedly attached to shaft I85 which, in turn, has suitable bearingengagement in frame member H5. Also attached to shaft I85 is a gear I86adapted to mesh with a pair of gears I81 and I89, these two latter gearshaving bearing engagement on a pin or shaft Ia. Also in meshingengagement with gears I01 and I03 is a gear I03 rigidly attached to oneend of shaft II, which in turn is suitably supported in bearingengagement with frame member II5. Rigidly attached to a shaft I050 is aring gear IIO, this ring gear and gears I06, I01, I03 and I03 forming adifferential gear system. Ring gear H0 is adapted to mesh with a gearIII rigid with 'screwthreaded shaft II2 which, in turn, is supported byframe II5. Shaft I22 is adapted to adjustably support link Ill.Operation of link Ill resultsin a corresponding operation of pointers 32and 33. The link and the pointer shaft 3a are connected by a -mechanismmore particularly shown in Figure l of my aforementioned prior patent.Since my aforementioned prior patent shows but a single pointer, it isnecessary that pointers 32 and 33 be operativelyconnected by suitablegear mechanism, this gear mechanism being shown in Figure 10 andcomprising a gear I22 integral with shaft II3la. Gear I22 is adapted tomesh with gear I23 rigid with shaft I24 which, in turn, is Sl1itablymounted for hearing engagement in the instrument. Integral with shaftI24 is a gear I23 adapted to mesh with gear, I28 which in turn isintegral with hollow shaft I21. Pointers 32 and 33 are also actuated bymeans of pressure responsive element I la, metallic link I5a. secondarylink ISa, flexible chain connection I'Ia corresponding to identicalparts in my aferementioned patent but identified therein without thesuffix a.

Coming now to the temperature compensating feature of the invention,pointers 32 and 33 are adapted to be compensated for ground temperatureaswell as the temperature existing at the instrument. The parts are sointerconnected that-actuation of the knob to tune in the groundtemperature receiver results in a simultaneous actuation of pointers 32and 33 as well as temperature reference mark Ila. This result isaccomplished by actuation of knob with gears 43 and 5| in mesh. Gear SIis adapted to mesh with the peripheral teeth of gear 62, the edge teethof which mesh with the edge teeth of gear 5'. Gear 5', in turn, hasteeth on the periphery thereof meshing with the peripheral teeth of gearII6, integral with shaft II. As previously pointed out, shaft II hasalso integral therewith gear I08 forming a part of the previouslydescribed differential.

Coming now to the actuation of temperature reference mark a, uponactuation of knob 45 it will be noted that gear 62 is integral with oneend of hollow shaft 63 freely rotatable on shaft MI and having suitablebearing engagement with frame member 30a. The other end of shaft 63 hasintegral therewith a gear 65 adapted to mesh with gear 66 suitablysupported in the instrument which, in turn, is in meshing engagementwith internal gear 61 carrying reference mark Ia. It will thus bereadily apparent that actuation of knob 45 results in the correspondingactuation of temperature reference mark 4Ia.

Pointers 32 and 33 are actuated by a suitable mechanism in response totemperature changes at the-instrument, to follow the teaching of myaforementioned prior patent, by a free air thermometer 34a, flexibleconnection 33a and Bourdon tube 30, which is connected to link H4 byconnection 28' and pin 29a. Operation of the Bourdon tube results in thecorresponding operation of the link II4 which, in turn, operatespointers 32 and 33 as previously described and particularly pointed outin my aforementioned of link I23 a rack I23 adapted to mesh with gearI30, integral with shaft I3I'. Shaft III,-

as will be noted, carries pointer 59a.

The toggle switch 43 consists of a body portion 54 detachably screwed tothe altimeter M, a yoked throw 55, two throw collars I56 and attachingpins 51, fixed to the shaft extension 43 and binding posts 53. Operationthereof has been previously described above;

My invention permits the following simple operations to be' accomplishedby an airman in setting his pressure altimeter in flight. Referring toFig. 3 the airman rotates knob 25 slightly either way until the signallamp 35 lights. The

setting is automatically made to conform to the existing conditions onthe ground. Should the airman require the ,maximum accuracy, theindication may be corrected by the use of any suit able computer. To usethe computer, the temperature aloft and the temperature at the ground isrequired. He reads the temperature aloft from the pointer of thethermometer 33 shown in Fig. 5. To get the temperature at the ground, herotates knob 39, Fig. 5 until the signal lamp 35 lights. He then readsthe ground temperature on the temperature scale adjacent to thereference mark 4 I. a

In using a temperature-pressure altimeter with my invention, the abovenoted operations are greatly simplified. Knob 45 is pushed in androtated until the signal lamp 35 lights, thus indicating that zerosetting of pointers 32 and 33 has been accomplished for temperature. Theknob 43 is then permitted to come out by thepressure of the spring 41.The signal lamp 36 will thereafter. go out. The knob is again rotateduntil signal lamp 33 lights, thus indicating that additional zerosetting of pointers 32 and 33 has been accomplished for "pressure".Complete zero setting" is then accomplished and true altitude will beindicated.

Although the description is specific to the illustrations, it is to beunderstood that there may be departures therefrom which will still beclaim as new and desire to secure by Letters Patent of the United Statesis:

1. An apparatus for determining the altitude of an aerial body above agiven reference lev comprising, means located at said reference levelfor generating radio frequency oscillations in accordance withpredetermined characteristics of the atmosphere, means carried by saidaerial body for tuning said oscillations, further carried means forindicating like predetermined characteristics of the atmosphereincluding zero setting adjustment, and connecting means between saidtuning means and zero setting adjustment whereby tuning of said receivereffects zero setting adjustment.

2. An apparatus for determining the altitude the atmosphere, manuallyadjusted means carried by said aerial body for tuning said oscillations,

further carried means for indicating like predetel-mined characteristicsof the atmosphere including zero setting adjustment, and connectingmeans between said tuning means and zero setting adjustment wherebytuning of said receiver automatically effects zero setting adjustment.

3. An apparatus for determining the altitude of an aerial body above agiven reference level comprising, radio transmission means located atsaid reference level self-adjusting in accordance with changes inpredetermined atmospheric characteristics, means carried by said aerialbody for indicating change in like atmospheric characteristics includingzero setting adjustment, and further carried means referable to saidradio transmission means and interconnected with said zero settingadjustments such that bringing of said further carried means into tunedrelationship with said radio transmission means automatically effectszero setting of said change indicating means.

4. An apparatus for determining the altitude of an aerial body above agiven reference level comprising, radio transmission means located atsaid reference level self-adjusting in accordance with both pressure andtemperature changes, meanscarried by said aerial body for indicatingchange in atmospheric pressure and temperature including zero settingadjustments, and further carried means referable to said radiotransmission means and selectively interconnectable with said zerosetting adjustments such that bringing of said further carried meansinto tuned relationship with said radio transmission means automaticallyeffects zero pressure and temperature setting.

5. A system for determining the true altitude of an aerial body above agiven reference level comprising: a transmitter located at saidreference level, constituting means for generating a carrier wave at apredetermined radio frequency; means for varying the carrier frequencyin accordance with an atmospheric condition external to saidtransmitter; means carried by said aerial body for indicating likeatmospheric condition to that external to said transmitter, includingzero setting adjustment; and further means carried by said aerial bodyin remote radio communication with said transmitterand interconnected tosaid zero setting adjustment such that tuning of said further carriedmeans to said carrier frequency effects zero setting adjustment.

6. A system for determining the true altitude of an aerial body above agiven reference level comprising: a transmitter located at saidreference level, constituting means for generating a carrier wave at apredetermined radio frequency; means for varying the carrier frequencyin accordance with an atmospheric condition external to saidtransmitter; a second like transmitter similarly located; further meansvarying said second carrier frequency in accordance with a secondatmospheric condition external to said second transmitter; means carriedby said aerial body for indicating like atmospheric conditions to thoseexternal to said first and second transmitters, including zero settingadjustment, and further means carried by said aerial body capa ble ofremote radio communication with first one then the other of saidtransmitters and being substantially continuously interconnected withfirst one then the other of said zero setting adjustments such thatalternate tuning of said further carried means to first one then theother mined pressure-frequency of said carrier frequencies effectsalternate zero setting adjustment.

7. An apparatus for determining the altitude of an aerial body withreference to a given level, comprising: a radio signal transmitterlocated at said reference level, atmospheric-press'ure-responsi've meansfor varying the frequency of the transmitted signal in accordance with apredeterrelation, receiver means carried by said aerial body tunable toreceive and detect the transmitted radio signal, a pressure indicatorcalibrated to read altitude and having a zero setting means, and meansoperatively associated with said receiver and said zero setting meansfor tuning said receiver to the transmitted signal and adjust said zerosetting in accordance with a predetermined pressurefrequency relationcorresponding to the pressurei'requency relation of the groundtransmitter.

8. An apparatus for determining the altitude of an aerial body withreference to a given level, comprising radio signal transmission meansfor transmitting signals having frequencies, respectively, as a functionof thepressure and temperature of the atmosphere at said referencelevel, a radio receiving means tunable within a frequency band includingthe preselected frequency range of said transmitting means, a pres sureindicator calibrated to read altitude and having a zero pressure settingmeans and a zero temperature setting means, said setting means beingrespectively associated with said receiving means for establishingpressure and temperature settings upon tuning of said receiver to thetransmitted signals in accordance with predetermined pressure-frequencyand temperature-frequency relations corresponding to thepressure-frequency and temperature-frequency relations of thetransmission means.

9. In an apparatus for determining the altitude of an aerial body withreference to a given level, in combination, a pressure altimeterincluding zero setting adjustment for pressure, a radio receiver havingits frequency band based upon a preselected frequency range, means fortransmitting at frequencies within said range and at a frequency whichvaries in response to variations in atmospheric pressure conditions atsaid level, means for tuning said receiver to such frequency, and meanscorrelating said tuning means and said adjustment for effecting zerosetting ad- Justment of said altimeter when said receiver 15 tuned to afrequency corresponding to the pres sure condition of the atmosphere atthe reference level.

10. In an apparatus for determining the altitude of an aerial body withreference to a given level, in combination, a pressure-temperaturealtimeter including selective zero setting adjustments for pressure andtemperature, radio receiver means having a frequency band based 1 upon apreselected frequency range. means for r cans uassrrr.

